[Bug 1928200] Re: Prompt error message "Failed to unmount /oldroot" when shutdown or reboot

[Bin Li]

@daniel,

 Thanks for the solution, and it sounds good, could you help make merge
request to finalrd to ask the maintainer's idea?

 From my side, currently finalrd used by mdadm, I would like to remove
the dependency cause mdadm.

 In systemd/mdadm.shutdown from mdadm, it also do "mdadm --wait-clean
--scan".

$ cat ./debian/mdadm.finalrd
#!/bin/sh
# SPDX-License-Identifier: GPL-3.0-only
set -e

if [ "$1" = "setup" ]
then
    . /usr/share/initramfs-tools/hook-functions
    copy_exec /sbin/mdadm
    copy_exec /sbin/mdmon

    exit 0
fi

mdmon --all --takeover
mdadm -vv --wait-clean --scan
mdadm -vv --stop --scan

 Thanks!

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https://bugs.launchpad.net/bugs/1928200

Title:
  Prompt error message "Failed to unmount /oldroot" when shutdown or
  reboot

Status in OEM Priority Project:
  Fix Released
Status in systemd package in Ubuntu:
  Fix Released
Status in systemd source package in Focal:
  Fix Released

Bug description:
  [impact]

  root fs is not cleanly unmounted on shutdown

  [test case]

  create a file in /etc/binfmt.d/TestFormat.conf with the following
  content:

  :TestFormat:M::XX::/bin/true:F

  reboot the system, and then shutdown or reboot again, and watch the
  serial console for the error message:

  sd-umount[1334]: Failed to unmount /oldroot: Device or resource busy

  [regression potential]

  any regression would likely cause problems on shutdown and/or reboot,
  or may cause problems with unmounted root fs on shutdown/reboot

  [scope]

  this is needed only for f

  this is fixed upstream with PR 15566 which is included in v246, so
  this is fixed already in g and later

  this isn't reproducable on b

  [original description]

  On ubuntu 20.04, with latest kernel and systemd, it will show error on
  ThinkPad X1.

  sd-umount[1334]: Failed to unmount /oldroot: Device or resource busy

  systemd 245.4-4ubuntu3.6
  kernel: 5.8.0-53

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